In the current age of information, high-density and large-capacity memories have been developed with growing enthusiasm. Memories are required to have not only the capability of high-density, large-capacity and highly reliable storage, but also the capability of rewriting or the like. It is an optical disk that is known to satisfy these requirements.
Conventionally, in relation to an optical disk and an optical disk device for performing recording and reproduction with respect to the optical disk, for example, a CD, a MD, and a DVD have been commercialized, and many reports on relevant technologies have been made. Particularly, as an optical disk system including a magnetic field modulation type magneto-optical disk and a read-only disk that allows reproduction to be performed so that compatibility with the magnetic field modulation type magneto-optical disk is attained, a minidisk (a MD) and a driving device used for the minidisk have created a market.
Hereinafter, conventional minidisks (MD5) and a conventional driving device used for the minidisks will be described with reference to the appended drawings.
FIGS. 3A and 3B are cross sectional views schematically showing the configurations of optical disks in the form of a MD and an optical head and a magnetic head in an optical disk device for performing recording and reproduction with respect to the MDs. The following description is directed to the configurations and operations of the MDs, the optical head, and the magnetic head.
In FIG. 3A, reference characters 61 and 71 denote a recordable minidisk (hereinafter, referred to as a MD-PA and an optical disk cartridge housing the MD-RAM 61, respectively. In FIG. 3B, reference characters 62 and 72 denote a read-only minidisk (hereinafter, referred to as a MD-ROM) and an optical disk cartridge housing the MD-ROM 62, respectively.
In the MD-RAM 61 shown in FIG. 3A, reference characters 61a and 61c denote an optical disk substrate for transmitting a light beam that has passed through a light incidence surface 61b, which is formed of a transparent polycarbonate resin having a thickness of 1.2 mm, and a dielectric film that gives the effect of allowing optical enhancement to be attained, respectively. Further, reference characters 61d, 61e, and 61f denote a magneto-optical recording surface obtained by providing a magneto-optical recording medium mainly containing terbium, iron, cobalt, or the like on a surface to be irradiated with a light beam transmitted via the substrate 61a, a reflective film mainly containing aluminum, and a protective layer formed of an ultraviolet curable resin, respectively.
In the figure, reference characters 1, 2, and 3 denote an optical head having a light emitting part and a light receiving part, an objective lens mounted on the optical head 1, which focuses a light beam emitted from the light emitting part on the magneto-optical recording surface 61d, and a sliding-type magnetic head that is of a magnetic field modulation type, respectively. Further, reference character 4 denotes a lifter mechanism for regulating a positional relationship, i.e. spacing, between the magnetic head 3 and the MD-RAM 61. The optical disk 1, the objective lens 2, and the magnetic head 3 are allowed to move (seek) as a unit in a radial direction (a direction perpendicular to a plane on which the figure is drawn) 5 of the MD-RAM 61.
The optical disk cartridge 71 has openings on a side of the magnetic head 3 as well as a side of the optical head 1, each of which has a shutter (not shown) that can be opened and dosed.
The magnetic head 3 and the lifter mechanism 4 are operated in the following three operation modes.
In the figure, reference character 3a denotes a recording mode for the magnetic head 3. In the recording mode 3a, the magnetic head 3 that has been inserted through one of the openings of the optical disk cartridge 71 is sliding on the protective layer 61f of the MD-RAM 61. This operation requires a sliding member (a member to be brought into contact with the MD-RAM 61, not shown) of the magnetic head 3 to have sliding characteristics in which importance is placed on abrasion resistance or the like. The protective layer 61f also has a composition in which importance is placed on the sliding characteristics. For example, the protective layer 61f is coated with a silicone oil (such as polydimethyl silicone). Further, reference character 4a denotes a recording mode for the lifter mechanism 4 in which the magnetic head 3 is put into the recording mode 3a by the lifter mechanism 4. In the recording mode 4a, the lifter mechanism 4 is out of contact with the magnetic head 3.
In the figure, reference character 3b denotes a reproducing mode for the magnetic head 3. In the reproducing mode 3b, the magnetic head 3 is held so that a given spacing is provided between the magnetic head 3 and the protective layer 61f of the MD-RAM 61. Further, reference character 4b denotes a reproducing mode for the lifter mechanism 4 in which the magnetic head 3 is put into the reproducing mode 3b by the lifter mechanism 4. In the reproducing mode 4b, the lifter mechanism 4 is in contact with the magnetic head 3 to lift the magnetic head 3 to a predetermined level.
In the figure, reference character 3c denotes a mode (a cartridge insertion mode) for the magnetic head 3 in which the optical disk cartridge 71 housing the MD-RAM 61 is inserted into the optical disk device to be mounted in a mechanism (not shown). In the cartridge insertion mode 3c, the magnetic head 3 is held (retracted) so that a given spacing is provided between the magnetic head 3 and the optical disk cartridge 71 to avoid interference between them. Further, reference character 4c denotes a cartridge insertion mode for the lifter mechanism 4 in which the magnetic head 3 is put into the cartridge insertion mode 3c by the lifter mechanism 4. In the cartridge insertion mode 4c, the lifter mechanism 4 is in contact with the magnetic head 3 to lift the magnetic head 3 to a level higher than that in the reproducing mode 3b. 
In the MD-ROM 62 shown in FIG. 3B, reference character 62a denotes an optical disk substrate for transmitting a light beam that has passed through a light incidence surface 62b, which is formed of a transparent polycarbonate resin having a thickness of 1.2 mm. Further, reference characters 62d, 62e, and 62f denote a pit information surface formed on a surface to be irradiated with a light beam transmitted via the substrate 62a, a reflective film mainly containing aluminum, and a protective layer formed of an ultraviolet curable resin, respectively.
In the figure, as in the case of the MD-RAM 61 shown in FIG. 3A, reference characters 1, 2, and 3 denote an optical head, an objective lens, and a magnetic head, respectively. Further, reference character 4 denotes a lifter mechanism for regulating a positional relationship, i.e. spacing between the magnetic head 3 and the MD-ROM 62. The optical head 1, the objective lens 2, the magnetic head 3, and the lifter mechanism 4 are the same components as those of the optical disk device used in the case of the MD-RAM 61. The optical disk 1, the objective lens 2, and the magnetic head 3 are allowed to move (seek) as a unit in a radial direction (the direction perpendicular to the plane on which the figure is drawn) 5 of the MD-ROM 62.
Since the MD-ROM 62 is a read-only optical disk, the operation modes of the magnetic head 3 and the lifter mechanism 4 do not include the following modes described with reference to the MD-RAM 61 shown in FIG. 3A: the recording mode 3a in which the magnetic head 3 is sliding on the protective layer 61f of the MD-RAM 61; and the recording mode 4a for the lifter mechanism 4 in which the magnetic head 3 is put into the recording mode 3a by the lifter mechanism 4. In terms of the mechanism of the optical disk device, there is no difference between the cases shown in FIGS. 3A and 3B, and thus it is possible to put the lifter mechanism 4 into the recording mode 4a. However, the optical disk device is set so that the lifter mechanism 4 is not operated in the recording mode 4a when the MD-ROM 62 is mounted in the optical disk device.
Accordingly, the optical disk cartridge 72 is structured to have an opening only on a side of the optical head 1, which has a shutter (not shown) that can be opened and closed, and not to have an opening on a side of the magnetic head 3.
In addition, since the recording mode 3a is not included in the operation modes for the magnetic head 3, it is not required at all that the protective layer 62f of the MD-ROM 62 has a composition in which importance is placed on the sliding characteristics as in the case of the protective layer 61f of the MD-RAM 61.
In FIG. 3B, reference character 3b denotes a reproducing mode for the magnetic head 3. In the reproducing mode 3b, the magnetic head 3 is held so that a given spacing is provided between the magnetic head 3 and the optical disk cartridge 72 as well as the protective layer 62f of the MD-ROM 62. Further, reference character 4b denotes a reproducing mode for the lifter mechanism 4 in which the magnetic head 3 is put into the reproducing mode 3b by the lifter mechanism 4. In the reproducing mode 4b, the lifter mechanism 4 is in contact with the magnetic head 3 to lift the magnetic head 3 to a predetermined level.
In the figure, reference character 3c denotes a mode (a cartridge insertion mode) for the magnetic head 3 in which the optical disk cartridge 72 housing the MD-ROM 62 is inserted into the optical disk device to be mounted in a mechanism (not shown). In the cartridge insertion mode 3c, the magnetic head 3 is held (retracted) so that a given spacing is provided between the magnetic head 3 and the optical disk cartridge 72 to avoid interference between them. Further, reference character 4c denotes a cartridge insertion mode for the lifter mechanism 4 in which the magnetic head 3 is put into the cartridge insertion mode 3c by the lifter mechanism 4. In the cartridge insertion mode 4c, the lifter mechanism 4 is in contact with the magnetic head 3 to lift the magnetic head 3 to a level higher than that in the reproducing mode 3b. 
The following description is directed to recording and reproducing operations of the MDs.
In the recording operation for the MD-RAM 61, as shown in FIG. 3A, the magnetic head 3 is put into the recording mode 3a. Then, a modulated magnetic field is applied from the magnetic head 3 to the magneto-optical recording surface 61d based on a modulating signal, and DC (direct current) light of a relatively high power level is emitted from the optical head 1, so that a minute beam spot is formed on the magneto-optical recording surface 61d using the objective lens 2. This allows a magneto-optical information signal to be recorded by a so-called magnetic field modulation recording method.
In the reproducing operation for the MD-RAM 61, the magnetic head 3 is put into the reproducing mode 3b. Then, while the magnetic head 3 is not energized, DC (direct current) light of a relatively low power level is emitted from the optical head 1, so that a minute beam spot is formed on the magneto-optical recording surface 61d using the objective lens 2. This allows the light beam reflected from the magneto-optical recording surface 61d to be reproduced as a magneto-optical information signal due to the so-called Kerr effect.
In the reproducing operation of the MD-ROM 62, as shown in FIG. 3B, the magnetic head 3 is put into the reproducing mode 3b. Then, while the magnetic head 3 is not energized, DC (direct current) light of a relatively low power level is emitted from the optical head 1, so that a minute beam spot is formed on the pit information surface 62d using the objective lens 2. This allows the light beam reflected from the pit information surface 62d to be reproduced as a pit information signal obtained by detecting the presence or absence of a pit based on the so-called variation in intensity of the light beam.
As described above, the recording and reproducing operations with respect to the MD-RAM 61 and the reproducing operation with respect to the MD-ROM 62 can be performed by the same optical disk device.
In the above description, other components of the optical disk device such as a motor, a circuit, and a disk loading and holding mechanism are not described nor shown in the figures since they are not related directly to the present invention.
The aforementioned configurations of the conventional MDs and the conventional optical disk device have presented the following problems.
In the optical disk device used for the MD-RAM 61 and the MD-ROM 62 shown in FIG. 3, it is required that the lifter mechanism 4 be operated in three operation modes, i.e. the recording mode 4a, the reproducing mode 4b, and the cartridge insertion mode 4c. This has led to the problems of a complicated mechanism design, an increased number of components, more room required for the lifter mechanism 4, and a complicated system control. Generally, it results in an increase in manufacturing cost to develop measures directed to the aforementioned problems to provide an optical disk device for performing recording and reproduction with respect to a compact MD, which has been disadvantageous.
Furthermore, the aforementioned configurations also have presented the following problem. When reproduction is performed with respect to the MD-RAM 61 and the MD-ROM 62, the lifter mechanism 4 is put into the reproducing mode 4b. In the reproducing mode 4b, the lifter mechanism 4 is in contact with the magnetic head 3 to lift the magnetic head 3, and thus the optical head 1 hardly can perform a seeking operation at a high speed in the disk radial direction 5. In the seeking operation performed in reproduction, it is required that the magnetic head 3 slide on the lifter mechanism 4. However, in a state where two components are moving relative to each other while being mechanically in contact with each other, mechanism resonance, vibration caused by external disturbances, stick-slip, and the like are caused to affect even a servo signal of the objective lens 2. This has led to a problem of difficulty in realizing a high-speed seeking operation. On the other hand, when recording is performed with respect to the MD-RAM 61, the lifter mechanism 4 is out of contact with the magnetic head 3, and thus the aforementioned problem does not arise in a seeking operation performed in recording. Instead, the magnetic head 3 is brought to a state of simply sliding on the protective layer 61f under a condition of considerably high sliding characteristics.
Moreover, when an optical disk device (a drive) is configured so as to be adaptable to a partially recorded optical disk (a partial ROM) that even meets the MD Standards, controlling of the lifter mechanism 4 becomes more complicated, and the technical problem of the difficulty in realizing the high-speed seeking operation becomes more serious.
In addition, as shown in FIG. 3, while the optical disk cartridge 71 for the MD-RAM 61 is structured so as to have the openings and the shutters on the side of the magnetic head 3 as well as the side of the optical head 1, the optical disk cartridge 72 for the MD-ROM 62 is structured so as to have the opening and the shutter only on the side of the optical head 1 and not to have the opening and the shutter on the side of the magnetic head 3. This has led to a major problem of the difficulty in achieving commonality between the optical disk cartridge 71 and the optical disk cartridge 72.